Elevator systems most commonly include a single elevator car within a hoistway. It has been proposed to include two elevator cars within a single hoistway. While such a proposal can be found in the patent literature dating back many years, it has been uncommon to implement such a system. There are various challenges associated with attempting to include two elevator cars within a single hoistway.
For example, it is necessary to address the situation where a hoistway door is open. In traditional, one elevator car systems, a safety chain is installed along the hoistway. A door lock at each hoistway door is associated with a relay switch along the safety chain. When all of the doors are closed, all of the relay switches are also closed. The elevator car is permitted to run provided that all of the relay switches are closed, which indicates that all of the doors are closed. Whenever one of the doors opens, the corresponding relay switch contacts open, which interrupts the safety chain circuit. Under such circumstances, the elevator car is not permitted to move.
When two elevator cars are introduced into a single hoistway, it would be undesirable to stop both elevator cars in the event that a hoistway door is open for servicing a passenger on one of the elevator cars. If the traditional, one elevator car approach were used, any time the safety chain circuit were interrupted, both cars would have to stop. A better solution would be to allow one of the cars to continue moving while the other is stopped at the location of an open door.
One proposed arrangement to address this issue is shown in United States Patent Application Publication No. US 2005/0082121. That document discloses an arrangement where a safety control determines elevator car position data and door lock data and then establishes shaft regions in which each elevator car is safely movable based on that data. Another approach is shown in U.S. Patent Application Publication No. U.S. 2006/0175135. That document includes using two independent safety circuits, one for each of the elevator cars. While each of these proposals theoretically allow for one elevator car to continue moving while the other is stopped within the same hoistway, those skilled in the art are always striving to make improvements. It would be beneficial to provide a less complicated and less expensive solution that allows for controlling two elevator cars within a single hoistway in the event that a hoistway door is open.